Hi,

probably 95% + of the time the connections work. ( it may not be comfortable but it works).
That being said, when I'm booking a connection from Edi to a long haul destination , I like to come down to Heathrow the night before.
For European destinations I am slightly hesitant to book a connection less than 2hrs but usually that is not a problem ( even on the first flight down from EDI , you will miss the first flights to many European destinations so you will have a wait till lunchtime or afternoon in any event)
Later domestics do seem to have more delays ( my feeling) so would allow more time if needed.

Regards

TBS